Power transmission lines are used to transmit power from power generation plants to substations and other power consumption facilities. The power transmission lines are suspended from towers or poles using several types of well-known installations. The horizontal-V is one of those well-known installations. As shown in FIG. 1, a strut insulator (1) extends horizontally from a utility pole (2) and a stay insulator (3) extends at an angle from a point on utility pole (2) above the point where strut insulator (1) is connected to pole (2). The two insulators are joined together at their distal ends, and a conductor (4) is suspended from the joined distal ends. The appearance of the strut and stay insulators mounted on the pole is what gave rise to the horizontal-V name.
The weight of the conductor (4) and other hardware (e.g., anchor shackle, suspension clamp, link, armor rod, and the like) results in stay insulator (3) being in tension and strut insulator (1) being in compression. As such, different insulator structures are usually employed for the stay and strut insulators; the former must withstand tensile forces, and the latter must withstand compressive forces.
It is necessary to mount the insulators on the pole in a manner that will allow the fixed ends of the insulator to pivot in the event of line movement. For example, a wind gust may cause the transmission line to move vertically (up and down in the plane of FIG. 1) as well as longitudinally (in and out of the plane of FIG. 1). It is preferred that the mounting structures used to connect the insulators to the pole pivot at the fixed ends of the insulators in order to relieve any impact shock in the insulator due to movement of the conductor. Otherwise, extreme movement of the conductor could result in damage to the insulators.
It is relatively easy to connect the stay insulator to the pole since that insulator is subjected mainly to tensile forces. One connection method uses an anchor shackle (5) connected to the tower or an extension thereof. The anchor shackle is connected to a similarly configured metal fitting (6) on the stay insulator. This arrangement allows adequate vertical and longitudinal pivoting at the fixed, tower end of the stay insulator.
The strut insulator presents unique mounting problems, however, due to the compressive forces imposed by the weight of the conductor and associated hardware. Various types of mounting assemblies (7) have been used to connect the strut insulator to the pole. FIGS. 2a and 2b show top and side views, respectively, of one example of such a mounting assembly.
The mounting assembly shown in FIGS. 2a and 2b includes a base (20) that is secured directly to a utility pole (2) by fastening bolts (B) through holes (21) passing through the vertical leg (22) of base (20). A coupling plate (23) is pivotally mounted on base (20) via a vertical oriented bolt (24) extending through holes (25) and (26) passing through horizontal legs (27) and (28) of base (20). The bolt (24) defines an axis about which the strut insulator can pivot in the longitudinal direction (in and out of the plane of FIG. 2b). A bolt (29) passes through the clevis fitting (30) of the strut insulator, and through coupling plate (23) to connect the strut insulator to the mounting assembly. Bolt (29) defines an axis about which the strut insulator can pivot in the vertical direction (up and down in the plane of FIG. 2b).
While this mounting assembly provides the necessary longitudinal and vertical pivot axes for the strut insulator, it provides insufficient space between base (20) and coupling plate (23) for the bolts used to mount the assembly to a utility pole. Specifically, in order to insure reliable connection to utility pole (2), the pole mounting bolts (B) extending from pole (2) to receive the base (20) of the mounting assembly is preferably capped with locking means (e.g., a double nut, lock washer, cotter pin, etc.). As such, bolts (B) necessarily extend a relatively large distance beyond the surface of the vertical leg (22) of base (20). The extension of pole mounting bolts (B) often times interferes with the attachment and pivotal movement of coupling plate (23).
Installation of the mounting assembly shown in FIGS. 2a and 2b to utility pole (2) also tends to be cumbersome, since the mounting holes (21), positioned within the confines of vertical legs (27) and (28) of base (20), can be difficult to access. Moreover, assembly of vertical bolt (24) requires an additional step, especially since a nut or cotter pin is usually employed to retain bolt (24) within holes (25) and (26) formed through base (20).